It's been a few days of experimentation but I'm at the point now where I'm committing to the A-5 and the original subject.
My first attempt at creating resin casts using the upper bulges was a fail for 2 reasons. One was that the bulges aren't quite the right shape. The second is that I used the wrong casting material as it's been so long that I've done this and I had two materials to chose from. I chose the wrong one - it ended up shrinking after I poured in the resin, resulting in some hideous looking casts which went straight into the trash. Below is the original mould casting set up using the wing uppers. This set up was unsuccessful.
I then went back to the idea of making a balsa master (I never did find the first one). Below you can see the process whereby I traced the shape of the bulge onto masking tape using a scale drawing as my basis. The tape was then cut out and stuck onto a block of balsa which I then shaped with a scalpel and sandpaper.
The balsa master was then pressed into plasticine per Wojtek's suggestion. I made 4 of these.
The 2 part resin was then mixed and I cast the 4 bulges. Though just 2 are needed, I made double in case one or two didn't turn out. The resin I have is clear so it's hard to see.
After a couple of days, the resin casts are popped from the mould. They look like this before being cleaned up and the plasticine is still stuck to this one in spots.
After the piece was cleaned up, the excess was cut away and the piece was thinned by running it over coarse sandpaper. Some final smoothing was then done. Once the casting was cleaned and shaped and found to be something that I could work with, it was time to commit to the A-5 version by carving away the incorrect bulges.
A trial fitting of the new blister shows that this will work. As you can see from the drawing adjacent to the kit parts, I will now need to fill some of the incorrect panel lines of the access hatch and rescribe them to suit the new blister.
At this stage the panel lines have been filled with primer and set aside to cure over night. In the meantime I will do some final shaping of the blisters to make sure they fit flush to the curved surface. I will then sand down the filled panel lines, scribe new ones, and then glue on the new blisters.
This is a big step and has been holding me back from getting on with this build. Once these blisters are on, I should get going in earnest. Thanks for stopping by guys.